In many roofing applications, for example in large, flat commercial roof decks, the roofing substrate is a concrete, light weight concrete, wood, gypsum, wood fiber or steel roof deck. The roofing membrane is used to seal and protect the roof deck from environmental weather conditions and is placed over insulation boards, which provide insulative qualities. The insulation boards are typically secured to the roofing substrate or roof deck via an adhesive composition or fasteners. The roofing membrane may be made of various materials, such as polymeric materials including EPDM (ethylene propylene diene M-rubber), Mod Bit (Modified Bitumen), TPO (thermoplastic polyolefin), or polyvinyl chloride (PVC). The roofing membrane may also be a composite material that includes EPDM or TPO. The roofing membrane is adhered overtop insulation boards or panels using an adhesive composition such as mopping asphalt (typically Type III or Type IV) or other conventional adhesive compositions. These adhesives are applied to both the roofing membrane and the substrate.
A conventional adhesive composition used to adhere the roofing membrane to the roof deck or other substrate includes the use of an elastomer dissolved in solvent, such as, for example, a polychloroprene rubber in an acetone or toluene solvent. However, typical polychloroprene rubber adhesives are solvent based and contain high (>250 g/L) levels of volatile organic compounds (VOC) content. These adhesives cannot be sold in areas where federal, state or local regulations prohibit the use of such high VOC adhesives. Other polychloroprene rubber adhesives use water as a solvent. While useful for their intended purpose, however, these water based adhesives may have issues regarding temperature restrictions, long curing times and odor concerns. In addition, these adhesives are contact adhesives that require full coverage between the substrate and the membrane, which makes it difficult to re-position the membrane after contact with the adhesive. Accordingly, solvent and water based elastomer adhesives must be applied to both the substrate and the roofing membrane and cover substantially the entire surfaces of the adhering components.
Accordingly, there is room in the art for adhesive compositions in roofing applications that exhibit favorable properties, such as sufficient adhesive strength, shelf life, cure time, tack, and that are easily applied including the ability to re-position the membrane after contact with the adhesive.